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An Emergency Slide Inflated into the Cabin of a United Airlines 737. What Went Wrong? Plus: Evacuation Etiquette, and Everything You Need to Know About Doors.

June 30, 2014

MUST BE a slow news day. That would help explain the media’s feeding frenzy in response to the Sunday night incident in which an emergency escape slide deployed inflight on a United Airlines 737. There were no injuries and the jet landed safely.

Sure, an inflight deployment of an escape slide is highly unusual (it also occurred aboard a Boston-bound JetBlue flight in 2013) and potentially dangerous. The slides are large, and when they inflate, they do so with considerable speed and force. One could, conceivably, cause substantial damage.

But this is unlikely, and contrary to what some of the the hysterical new coverage might imply, the flight was in no danger of crashing.

The biggest hazard would have been to any passengers or crew who happened to be standing near, or passing by, the door. He or she could easily be knocked unconscious, or worse, or find themselves pinned against the wall, floor, or other part of the cabin. Fortunately in both the United and JetBlue incidents, nobody was in the way.

Normally the escape slides are contained within the door, inside that boxy lower compartment where it sometimes says DO NOT SIT HERE along the top edge. Once the flight attendants “arm” the doors prior to push-back, the slides will deploy and inflate automatically — outward, of course — any time a door is opened. There is no separate control for the slides; they are activated by the action of the door itself. It’s possible that jiggling a door handle or otherwise messing with the slide housing (again, that DO NOT SIT HERE warning) could cause a slide to blow, but that’s unlikely. What happened aboard United and JetBlue seems to indicate some sort of internal malfunction.

While we’re at it, should you ever need to jump down one of those slides for real during an evacuation, please don’t bring your carry-on items with you. Those escape slides are very steep. They are not designed with convenience in mind. They are there to get a planeload of people out of, and away from, the aircraft as quickly as possible — without their belongings. You’ll be coming down — from over two stories high in the case of a widebody jet — at a rapid clip, with others doing the same in front of you and right behind you.

And since we’re talking doors, I’ll take this opportunity to remind people that you cannot – repeat, cannot – open the doors or emergency hatches of an airplane in flight. You can’t open them for the simple reason that cabin pressure won’t allow it. Think of an aircraft door as a drain plug, fixed in place by the interior pressure. Most aircraft exits open inward. Some retract upward into the ceiling; others swing outward; but they open inward first, and not even the most musclebound human will overcome the force holding them shut. At a typical cruising altitude, up to eight pounds of pressure are pushing against every square inch of interior fuselage. That’s over 1,100 pounds against each square foot of door. Even at low altitudes, where cabin pressure levels are much less — a meager 2 p.s.i. differential is still more than anyone can displace — even after six cups of coffee and the aggravation that comes with sitting behind a shrieking baby. The doors are further held secure by a series of electrical and/or mechanical latches.

So, while I wouldn’t recommend it, unless you enjoy being pummeled and placed in a choke-hold by panicked passengers, a person could, conceivably, sit there all day tugging on a door handle to his or her heart’s content. The door is not going to open (though you might get a red light flashing in the cockpit, causing me to spill my Coke Zero). You would need a hydraulic jack, and TSA doesn’t allow those.

On the 19-passenger turboprop I used to fly, the main cabin door had an inflatable seal around its inner sill. During flight the seal would inflate, helping to lock in cabin pressure while blocking out the racket from the engines. Every now and then the seal would suffer a leak or puncture and begin to deflate, sometimes rapidly. The resultant loss of pressurization was easily addressed and ultimately harmless, but the sudden noise — a great, hundred-decibel sucking sound together with the throb of two 1,100 horsepower engines only a few feet away — would startle the living hell out of everybody on the plane, including me.

I am, once again, going to take issue with this. I believe one should take one’s medications and medical devices if they can be grabbed quickly. My carry on, these days, consists of a bad with my CPAP machine my medications. I can’t sleep without the CPAP and I risk death not taking my medication for even for as little as 24 hours. Depending on where we are deplaning, replacing the CPAP and medication can take from days to weeks. i don’t check these items because of the need of them and the dire consequences of losing them. As I weigh 320 pounds, I suspect the additional 5 pounds of my CPAP bag will not make a measurable difference on the slide, but its loss would wreak havoc on me for days afterwards. Thus, I would grab that bag and take it with me.

I don’t think people should grab carryon that contains clothes, cameras, computers, or other replaceables, but items that will impact one’s health — medications, prosthetic devices, medical devices — seem like an exception to the rule. I see little point to deplane quickly to save my life only to die of a stroke or diabetic comma 8 hours later.

Neither of them give a full, accident-report type of explanation, but…

It seems that the pilot either fully or partially depressurized the cabin. Given that he did that above 12,000 feet (where pressurization or supplementary oxygen is required), i’m *assuming* that the pilots must have had their own supplementary oxygen.

And again this is assumption, they were out of range of an airfield, and were so scared that they felt the only way to deal with this guy was to try to knock him out by oxygen deprivation. An *extreme* step. Potentially deadly to anyone without oxygen.

But, I suppose, if you’re in a King Air, where there’s no door to block access to the pilots, and there’s a crazy man who’s already tried, twice, to open the cabin door, what other choice did they have? I’m sure they were having a WTF? moment.

I don’t have any experience with the King Air, so I have no idea how that door works. But I suspect it doesn’t have the same passenger-fault tolerance that an airliner does.

From what I understand a person haas to leap out onto to the slide during an emergency evacuation. I’m curious whether an elderly or disabled people can safely evacuate through an evacuation slide? My moms reaching an age where her legs just aren’t functioning like they used to.

Leaping onto a slide is preferred. Leaping onto a slide is ideal. Not leaping onto a slide slows down the evacuation for everyone behind the non-leaper. That does not, however, mean that it is impossible to go down a slide without leaping. It just takes longer.

I am physically disabled myself and legally blind. Your mother probably is more disabled than me but she can ‘crawl to the disarmed door and sit on the slide, go over the bump and slide down to the bottom. Usually the pilot, a flight attendant or a passenger will be down at the bottom to assist her getting off the slide into the raft or to where the plane isn’t going to harm her. The flight attendant usually hurrys up the passengers before they slide down as the passengers are their main priority. They could help your mum down.

In April, 2009, a man in northern Canada committed suicide by opening the door in a small plane and jumping. There are conflicting reports in the media as to the altitude,The Guardian reported 33,000 feet, The Star reported 7,000 meters, a difference of about 10,000 feet. Both papers reported that there was a loss of pressure when the door opened.

I’m european, so it’s a bit difficult for me to follow the American calculations, but have you ever tried to open a door against 1mbar of pressure differential?

1mbar is the air-pressure difference you’d get from about 10m (30 feet) of height difference (at sea level, you’d need 4 times that at FL380).

I have…. “The door is locked”. “No it is not”. “Yes it’s locked”. “no really it is not”. The force is so much bigger than what you’re used to that it seems as if it is locked. Absolutely no movement. At 1mbar you CAN open it if you put aside your normal “i don’t want to break it” instincts. Anything more… I don’t think so.

At FL380, the pressure differential with the cabin pressure is about 500 mbar. The force required to open it against such pressure is on the order of 5-10 tonnes. So, yes… you can’t open that in flight…. 🙂

My point being that when the plane lifts off, within seconds the pressure differential could be high enough to prevent opening of the doors by human force. (but the air-pressure might still follow outside air pressure, depending on how the pilot has configured his cabin pressure).

I’ve logged the cabin pressure once. It was still “doing things” after we landed. If you’d put the cabin pressure at 2mbar above “outside” you’d have an extra “lock the doors as long as the plane is in one piece” safety. On the other hand, some mishaps might require opening the doors even if the plane is still airtight…. I don’t know what is common practise or what the FAA and friends prescribe… Patrick?

I don’t understand, given all you said about why you’re never going to get a door open at altitude, you could also say, “The slides are large and powerful and one could, conceivably, force open a door.” If the door *must* open inward first, how could that ever happen?

I second your admonition to leave luggage behind. Sometime in the 1970s my aunt was on an airliner that had an emergency and had to evacuate the passengers via slide. She said she went down so fast that the friction melted her pantyhose to her legs.

I went and changed that paragraph. It was confusing, as you note. My point was that with enough strength a slide could, conceivably, wrench a door right through its frame — or, on those types of doors that do NOT open inward first, otherwise force it open. Maybe, possibly.

At FL380 they had a pressure differential of around 8-9 psi. The door area is 72″x36″. Bottom line, that slide will do exactly nada to the door.

The real danger IMHO is the slide pinning somebody against the wall or ceiling. And as far as I know, there is no simple/controlled way to release the pressure in the slide from within the cabin. The crew would likely have to resort to more drastic methods. Sharp knives are hard to come by in flight. Fire axe maybe?

There have been problems with Beech 1900 doors and flights I’ve been on had a crew member use a flashlight to check the door before leaving the gate. On April 24, there was a Wasaya Airways in flight door opening. Landed safely.

TSB Report#A14C0061: C-FWXL (a Beech 1900, operating as Wasaya 985) had departed Sachigo Lake, ON for Sioux Lookout. Shortly after takeoff the crew heard a wind noise. The crew checked the caution panel but no warning lights were observed. A crew member was about to check the main cabin door to ensure that it was latched, when it popped open approximately 6 inches, and a door warning light illuminated. QRH items were carried out, the passengers were briefed, and the flight declared an emergency on the local frequency and diverted back to the Sachigo Lake airport. While the door was open approximately 6 inches the door restraining cable struck the left propeller. As the aircraft slowed on approach, the door opened further to point where it was approximately 90 degrees to the fuselage. When the aircraft touched down, the door opened fully and contacted the runway surface. The aircraft was taxied clear of the runway and the passengers were deplaned. There were no reported injuries. The aircraft sustained damage to its left propeller and main cabin door. The aircraft has been removed from service for inspection and clearance to ferry to a repair facility. Previously there were 2 similar NTSB occurrences NTSB FIles C)425201412000 and DEN031A147.